Multi-layer absorbent composite

ABSTRACT

Disclosed is an absorbent structure comprising first and second surge management layers and an absorbent layer located between said first and second surge management layers. The first surge management layer comprises synthetic polymeric fibers and the second surge management layer comprises hydrophilic fibers. The density of the absorbent layer is greater than the density of the first and second surge management layers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an absorbent composite, particularly toan absorbent composite which is useful in personal care products.

2. Description of the Related Art

Personal care products for the absorption of body fluids are known. Suchproducts include adult incontinence products, diapers, training pants,feminine care products, wound dressings and the like. As a general rule,such personal care products generally comprise an amount of a cellulosicfiber such as wood pulp fluff. Wood pulp fluff is known to be a suitableabsorbent for body fluids. As a general rule, 1 gram of wood pulp fluffis able to absorb from about 5 to about 8 grams of a discharged bodyfluid such as urine. A personal care product such as an infant diaper,generally has an absorbent capacity of at least about 200 to 400 gramsof urine. Thus, when such an infant diaper is formed from wood pulpfluff, a relatively large quantity of wood pulp fluff must be employed.

In order to reduce the amount of wood pulp fluff and the correspondingbulk of such an infant diaper, it is known to include high absorbencymaterials known in the art as superabsorbents. Such high absorbencymaterials are generally capable of absorbing at least about 10,preferably at least about 20, and up to 50 or more times their weight inwater. By incorporating such high absorbency materials in infantdiapers, it is possible to reduce the overall bulk of the diaper whilemaintaining its absolute absorbent capacity.

Nonetheless, the use of such high absorbency materials is not withoutproblems. For example, some high absorbency materials are known to causegel blocking. That is, as the high absorbency materials become swollenwith a liquid, they form a gelatinous mass which prevents the free flowof liquid therethrough. Thus, while the high absorbency materials may beable to absorb an initial insult, subsequent insults are unable to passthrough the now swollen high absorbency material. As a result,subsequent insults tend to pool and run off of the absorbent product.

Accordingly, a number of different structures have been proposed toalleviate or reduce the problems associated with incorporating highabsorbency materials in personal care products.

U.S. Pat. No. 4,699,619 issued Oct. 13, 1987, to Bernardin describes amultilayer absorbent composite having a first relatively low densitylayer and a second relatively high density layer underlying at least aportion of the first layer. A high absorbency material (superabsorbent)is described as being located between said first and second layers.

U.S. Pat. No. 4,102,340 issued Jul. 25, 1978, to Mesek et al. isdirected to a disposable article with a particulate hydrophilic polymerin an absorbent bed. Described is an absorbent pad comprising a fibrousstructure having an intermediate densified layer and a layer of highlyporous, loosely compacted batt on both sides of the densified layer. Oneof the batt layers is described as including a particulate,water-insoluble but water-swellable polymeric absorbent.

U.S. Pat. No. 4,269,188 issued May 26, 1981, to Nishizawa et al. isdirected to a disposable diaper. Disclosed is a disposable diaperincluding an absorbent material comprising a laminate wherein awater-absorbent polymer powder is fixed between two sheets of paper. Afluff pulp layer is located on both sides of the laminate containing awater-absorbing polymer.

While the structures described in the referenced patents have oftenproven beneficial, they have not completely solved the problemsassociated with the use of high-absorbency materials. In use, the woodpulp fluff generally serves to quickly absorb a discharged body fluid.The fluid is generally held in the pores of the fluff matrix. The highabsorbency material in the fluff matrix then absorbs the fluid and, ineffect, dewaters the fluff matrix. That is, the fluff serves to absorband hold surges (relatively large quantities applied relatively quickly)of body fluid until the high-absorbency material can absorb the bodyfluid. Moreover, many known personal care products employhigh-absorbency materials in relatively low quantities. This is becausethe cost of such high-absorbency materials is generally greater than thecost of a material such as wood pulp fluff. It is sometimes desirable toemploy a relatively high concentration of high-absorbency material whenforming a personal care product. As the concentration of high-absorbencymaterial increases in an absorbent product, the concentration of woodpulp fluff generally decreases. The high-absorbency materials are notgenerally able to absorb urine at the rate at which it is applied. Thismay lead to leakage in absorbent structures having high concentrationsof absorbent materials.

It is desired to provide an absorbent structure which may contain anabsorbent layer having a relatively high concentration ofhigh-absorbency material but which absorbent structure is capable ofquickly absorbing body fluids applied thereto.

SUMMARY OF THE INVENTION

The present invention concerns an absorbent structure. The structurecomprises a first surge management layer, a second surge managementlayer, and an absorbent layer located between the first and second surgemanagement layers. The first surge management layer comprises a fibrousweb comprising synthetic polymeric fibers. The first surge managementlayer has a basis weight of from about 20 to about 200 grams per squaremeter and a density of from about 0.01 to about 0.12 gram per cubiccentimeter. The second surge management layer comprises a fibrous webcomprising hydrophilic fibers. The second surge management layer has abasis weight of from about 20 to about 200 grams per square meter and adensity of from about 0.04 to about 0.20 gram per cubic centimeter. Theabsorbent layer comprises means for containing a high-absorbencymaterial and from about 50 to about 100 weight percent, based on totalweight of the absorbent layer, of a high-absorbency material containedby said means for containing a high-absorbency material. The absorbentlayer has a basis weight of from about 200 to about 1000 grams persquare meter and a density of from about 0.06 to about 0.40 gram percubic centimeter. The density of the absorbent layer is greater than thedensity of the first and second surge management layer and the densityof the first surge management layer is different than the density of thesecond surge management layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an absorbent structure according tothe present invention.

FIG. 2 is an exploded view of an infant diaper incorporating anabsorbent structure according to the present invention.

FIG. 3 is a cross-sectional view of one embodiment of an absorbent layerof the present invention.

FIG. 4 illustrates the apparatus for determining the Absorbency UnderLoad values of a high-absorbency material.

FIG. 5 is a perspective view of the apparatus used in conducting thefluid run-off determination.

FIG. 6 is a cross-sectional view of the apparatus used in conducting thefluid run-off determination.

FIG. 7 graphically illustrates the results set forth in Table 1.

FIG. 8 graphically illustrates the results set forth in Table 2.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns an absorbent composite. The absorbentcomposite comprises first and second surge management layers and anabsorbent layer located between the first and second surge managementlayers.

The first surge management layer comprises a fibrous web. The fibrousweb comprises synthetic polymeric fibers. The synthetic polymeric fibersmay be formed from any polymeric material capable of forming fiberswhich fibers can be formed into a fibrous web possessing the propertiesof the first surge management layer as discussed herein. Suitablepolymeric material from which the synthetic polymeric fibers of thefirst surge management layer may be formed include polyolefins, such aspolyethylene, polypropylene, and the like; polyesters such aspolyethylene terephthalate and the like; polyamides such as nylon 6,nylon 6,6, poly(iminocarboxylpentamethylene) and the like; acrylics, andmodified cellulosic material, such as cellulose acetate; as well asmixtures and copolymers thereof.

The synthetic polymeric fibers may be formed by meltblowing, through aspunbond process, by extrusion and drawing, or other wet, dry and meltspinning methods known to those skilled in the art. The syntheticpolymeric fibers from which the first surge management layer is formedmay have a discrete length or may be substantially continuous. Forexample, if the synthetic polymeric fibers are formed by meltblowing,the fibers may be substantially continuous (few visible ends). If thefibers are formed by extrusion and drawing to produce a tow, the tow maybe used as produced or cut into staple fibers having a length, forexample, of from about 25 millimeters to about 75 millimeters or shortcut into lengths of from about 1 millimeter to about 25 millimeters. Thesynthetic polymeric fibers may suitably have a maximum cross-sectionaldimension of from about 0.5 micrometer to about 50 micrometers asdetermined by microscopic measurement using an optical microscope and acalibrated stage micrometer or by measurement from Scanning Electronphotomicrographs.

The fibrous webs may be formed directly through a spunbond or meltblownprocess, or by carding or air-laying staple or short cut fibers. Othermethods of forming fibrous webs known to those skilled in the art may besuited for use in the present invention. The web may subsequently bebonded to enhance structural integrity. Methods of bonding fibrous websare known to those skilled in the art and include thermal bonding, pointbonding, powder bonding, ultrasonic bonding, chemical bonding,mechanical entanglement, and the like. The fibers may be homogenousfibers or may be a core/sheath or side-by-side fibers known to thoseskilled in the art as bicomponent fibers.

The first surge management layer may be formed from a single type ofsynthetic polymeric fiber or may contain synthetic polymeric fibersformed from different polymeric materials, having different fiberlengths or maximum cross-sectional dimensions. For example, the firstsurge management layer may comprise a mixture of (1) bicomponent fibershaving a polyethylene sheath and a polypropylene core which bicomponentfibers have a maximum cross-sectional dimension of about 20 micrometersand a length of about 38 millimeters and (2) polyester fibers(polyethylene terephthalate) having a maximum cross-sectional dimensionof about 25 micrometers and a length of about 38 millimeters. Fibers 1and 2 may be combined in a weight ratio of from 1:99 to 99:1. The fibersmay be uniformly mixed or may be concentrated at opposite planarsurfaces of the first surge management layer.

The first surge management layer of the present invention suitablycomprises from about 10 to 100 weight percent, beneficially of fromabout 20 to 100 weight percent, preferably of from about 25 to 100weight percent, and most preferably of from about 50 to 100 weightpercent synthetic polymeric fibers. In addition to the syntheticpolymeric fibers, the first surge management layer may contain fromabout 90 to 0 weight percent of a nonsynthetic polymeric fiber such aswood pulp fluff cotton linters, cotton, and the like.

In one preferred embodiment, the first surge management materialcontains synthetic polymeric fibers which are formed from a polymericmaterial having a high wet modulus. The importance of the modulus of amaterial is discussed in the book "Absorbency" edited by P. K.Chatterjee (Elsevier, N.Y., 1985). A polymeric material will beconsidered to have a high wet modulus when it has a wet modulus greaterthan about 80 percent of its dry modulus as determined by ASTM (AmericanSociety for Testing and Materials) test method D 2101-91 using modifiedgauge lengths. It is often desired to form the synthetic polymericfibers of the first surge management material from a polymeric materialhaving a high wet modulus because such materials generally form fibrouswebs which possess a relatively high degree of wet resiliency. The wetresilience of a fibrous web is related to the pore structure (whileunder a load) of the fibrous web. As will be discussed in greater detailbelow, it is often desired that the first surge management layer have arelatively high degree of wet resilience.

The pore structure (while under a load) of a fibrous structure formedfrom fibers of a polymeric material will, as discussed above, relate tothe wet and/or dry modulus of the constituent fibers. Wet modulus of theconstituent fibers should be considered for fibers that may likely bewetted during use. For the purposes of estimating the effect of load onthe pore structure of a fibrous structure formed from fibers of apolymeric material the tensile modulus of the fiber which can be relatedto the flexural rigidity of the fiber as shown in the book "PhysicalProperties of Textile Fibers" by W. E. Morton and J. W. S. Hearl (TheTextile Institute, London, 1975) can be used.

As a general rule, the polymeric materials from which the syntheticpolymeric fibers of the first surge management layer are formed will beinherently hydrophobic. As used herein, the term "hydrophobic" describesa material which has a contact angle of water-in-air of greater than 90degrees. The term "hydrophilic" refers to a material which has awater-in-air contact angle of less than 90 degrees. The water-in-aircontact angle is suitably determined as set forth in the book"Absorbency" edited by P. K. Chatterjee (Elsevier, N.Y., 1985). As usedherein, a polymeric material will be considered to be "inherently"hydrophobic or hydrophilic when the polymeric material, free from anysurface modifications or treatments, e.g., surface active agents, spinfinishes, blooming agents, etc., is hydrophobic or hydrophilic,respectively.

When the synthetic polymeric fibers of the first surge management layerare formed from a polymeric material which is inherently hydrophobic, itis often desirable to treat the fibers with a surface modifying materialto render the surface of the fiber hydrophilic. For example, asurfactant may be applied to the fibers.

The first surge management material suitably has a basis weight of fromabout 20 to about 200, beneficially of from about 30 to about 150, andpreferably of from about 35 to about 125 grams per square meter.

The first surge management material suitably has a density of from about0.01 to about 0.12, beneficially of from about 0.015 to about 0.1, andpreferably of from about 0.02 to about 0.08 gram per cubic centimeter.

The second surge management layer also comprises a fibrous web. Thefibrous web of the second surge management layer comprises hydrophilicfibers. The hydrophilic materials may be inherently hydrophilic such ascellulosic fibers such as wood pulp fluff, cotton linters, and the like;regenerated cellulose fibers such as rayon; or certain nylon copolymerssuch as poly(pentamethylenecarbonamide) (nylon-6)/polyethylene oxide.Alternatively, the hydrophilic fibers may be hydrophobic fibers whichhave been treated to possess a hydrophilic surface. For example, thefibers may be formed from a polyolefin material which is subsequentlycoated with a surface active agent such that the fiber itself ishydrophilic as described herein. Other methods of hydrophilizing fibersformed from hydrophobic materials are known and suited for use in thepresent invention.

Methods of providing inherently hydrophilic fibers such as wood pulpfluff are known. So to are methods of providing regenerated cellulosicfibers such as rayon. Hydrophobic fibers which can be treated to possessa hydrophilic surface are suitably formed in the same manner and fromthe same materials described above in connection with the first surgemanagement layer. If the hydrophilic fibers are hydrophobic fibers whichhave been treated to possess a hydrophilic surface, the fibers willsuitably have a fiber length and maximum cross-sectional dimension asset forth above. If the hydrophilic fibers are inherently hydrophilicsuch as wood pulp fluff, rayon, cotton, cotton linters and the like, thefibers will generally have a length of from about 1.0 millimeters toabout 50 millimeters and a maximum cross-sectional dimension of fromabout 0.5 micrometers to about 100 micrometers.

The fibrous web of the second surge management layer may be formed inthe same way as set forth above in connection with the first surgemanagement layer. The second surge management layer suitably comprisesfrom about 10 to 100 weight percent, beneficially from about 30 to 100weight percent, and preferably from about 55 to 100 weight percent ofhydrophilic fibers, preferably inherently hydrophilic fibers. Inaddition to the hydrophilic fibers, the second surge management layermay contain from about 90 to 0 weight percent of a high wet modulus,preferably inherently hydrophobic fibers. The second surge managementlayer may be formed from a single type of hydrophilic fiber or maycontain hydrophilic fibers having different compositions, lengths andmaximum cross-sectional dimensions. The second surge management layersuitably comprises a greater percentage of inherently hydrophilic fibersthan the first surge management layer. Specifically, the second surgemanagement layer suitably comprises at least about 10, beneficiallyabout 25 and preferably about 50 weight percent more inherentlyhydrophilic fibers than the first surge management layer when the firstsurge management layer comprises inherently hydrophilic fibers.

In one preferred embodiment, the second surge management layer is formedfrom air laid cellulosic fibers such as wood pulp fluff. Wood pulp flufffibers are preferred for use due to their ready availability and due tothe fact that the fibers are relatively inexpensive compared tosynthetic polymeric fibers.

The second surge management layer suitably has a basis weight of fromabout 20 to about 200, beneficially of from about 50 to about 150, andpreferably of from about 25 to about 125 grams per square meter.

The second surge management layer suitably has a density of from about0.04 to about 0.20, beneficially of from about 0.06 to about 0.16, andpreferably of from about 0.08 to about 0.14 gram per cubic centimeter.

An absorbent layer is located between the first and second surgemanagement layers. The absorbent layer is in liquid communication withthe first and second surge management layers. As used herein, theabsorbent layer will be considered to be in liquid communication withthe first and second surge management layers when a liquid can move fromeither the first or second surge management layer into the absorbentlayer. It is not necessary that the first and second surge managementlayers be in direct contact with the absorbent layer. That is,additional intervening layers can appear between the surge managementlayers and the absorbent layer. Nonetheless, a liquid must be able tomove from the first and second surge management layers, through oraround any such intervening layers and into the absorbent layer. Whenthis is possible, the first and second surge management layers will beconsidered to be in liquid communication with the absorbent layer.

The absorbent layer comprises means for containing a high-absorbencymaterial, and a high-absorbency material contained by such means forcontaining a high-absorbency material. The high-absorbency material ispresent in the absorbent structure in an amount of from about 50 toabout 100, preferably of from about 60 to about 95, and most preferablyof from about 70 to about 90 weight percent based on total weight of theabsorbent layer.

Means of containing high-absorbency materials are known to those skilledin the art. For example, the means for containing the high-absorbencymaterial may comprise a fibrous web, a porous sponge-like material, asubstrate to which the high-absorbency material is attached or adhered,multiple sheets of material between which the high-absorbency materialis located, and the like. Any means of containing of the high-absorbencymaterial is suited for use in the present invention.

As used herein, the term "high-absorbency material" refers to awater-swellable, generally water-insoluble material capable of absorbingat least about 10, desirably about 20, and preferably about 50 times ormore its weight in water. The high-absorbency material may be formedfrom organic material, which may include natural materials such as agar,pectin, and guar gum, as well as synthetic materials such as synthetichydrogel polymers. Synthetic hydrogel polymers include, for example,carboxymethyl cellulose, alkali metal salts of polyacrylic acid,polyacrylamides, polyvinyl alcohol, ethylene maleic anhydridecopolymers, polyvinyl ethers, hydroxypropyl cellulose, polyvinylmorpholinone, polymers and copolymers of vinyl sulfonic acid,polyacrylates, polyacrylamides, polyvinyl pyrridine, and the like. Othersuitable polymers include hydrolyzed acrylonitrile grafted starch,acrylic acid grafted starch, and isobutylene maleic anhydride copolymersand mixtures thereof. The hydrogel polymers are preferably lightlycrosslinked to render the materials substantially water insoluble.Crosslinking may, for example, be by irradiation or covalent, ionic, vander Waals, or hydrogen bonding. Suitable materials are available fromvarious commercial vendors such as the Dow Chemical Company, HoechstCelanese Corporation, Allied Colloid Inc., and Stockhausen Inc. Thehigh-absorbency material may be in the form of particles, spheres,flakes, fibers, rods, films or any of a number of geometric forms. Whenin the form of particles or spheres, it may be desired that theparticles or spheres have a maximum cross-sectional dimension of fromabout 10 micrometers to about 2000 micrometers, preferably from about 60micrometers to about 1000 micrometers.

In one embodiment it is desired that the high-absorbency material havethe ability to absorb a liquid while under a load. The ability of ahigh-absorbency material to absorb a liquid while under a load isquantified as the Absorbency Under Load (AUL) value. Specifically, theAUL value is the amount (in grams) of an aqueous solution containing 0.9weight percent sodium chloride, a gram of the high-absorbency materialcan absorb in 60 minutes under a load of 0.3 pound per square inch. As ageneral rule, it is desired that the high-absorbency material have anAUL value of at least about 10, desirably at least about 15, andpreferably at least about 25. A method by which the absorbency underload value is determined is set forth below in connection with theExamples.

The absorbent layer suitably has a basis weight of from about 200 toabout 1000, beneficially of from about 250 to about 750, and preferablyof from about 300 to about 500 grams per square meter. The absorbentlayer suitably has a density of from about 0.06 to about 0.40,beneficially of from about 0.12 to about 0.35, and most preferably offrom about 0.15 to about 0.30 gram per cubic centimeter.

The density of the absorbent layer is greater than the density of boththe first surge management layer and the second surge management layer.Suitably, the density of the absorbent layer is at least about 20percent, beneficially at least about 30 percent, and preferably at leastabout 40 percent greater than the density of both the first and secondsurge management layers. Further, the densities of both the first andsecond surge management layers are different. It is preferred that thedensities of the first and second surge management layers differ by atleast about 20 percent of the lowest density layer.

The absorbent structures of the present invention comprise at leastthree layers. From the above, it is clear that the three layers of theabsorbent structures of the present invention all have a differentdensity. Further, the absorbent layer has the highest density of thethree. Of the remaining two layers, the first and second surgemanagement layers, one will have an intermediate density (relative tothe absorbent layer and other surge management layer) and one will havea low density compared to the other surge management layer and absorbentlayer. The absorbent layer is located between the first and second surgemanagement layers. Thus, the density of the various layers of theabsorbent structure according to the present invention will be arrangedin one of the following orders: lowest density, highest density,intermediate density; or intermediate density, highest density, lowestdensity. For the purpose of this application, density of the first surgemanagement layer, second surge management layer and absorbent layerrefers to an average density of the layer being tested. That is, arepresentative number of density measurements are taken across thelength and width of the layer being tested. The individual densitymeasurements are then averaged to determine the average density. Thedensity is determined under a load of 0.05 pound per square inch (350pascal).

The absorbent structures according to the present invention are suitablefor use in disposable absorbent products such as diapers, trainingpants, adult incontinence products, feminine care products, wounddressings and the like. Methods of forming such absorbent products andthe absorbent products formed thereby are known to those skilled in theart and are described, for example, in the following U.S. Pat. Nos.:4,944,735 issued Jul. 31, 1990 to Mokry; 4,798,603 issued Jan. 17, 1989,to Meyer et al.; 4,710,187 issued Dec. 1, 1987, to Boland et al.;4,770,656 issued Sep. 13, 1988, to Proxmire et al.; and 4,762,521 issuedAug. 9, 1988, to Roessler et al.; as well as U.S. patent applicationSer. No. 07/757,778 filed Sep. 11, 1991, in the name of Proxmire et al.;and U.S. patent application Ser. No. 07/757,760 filed Sep. 11, 1991, inthe name of Hanson et al.; the disclosures of which are incorporatedherein to the extent they are consistent herewith.

The absorbent structures of the present invention suitably form theabsorbent core of the disposable absorbent products. Such an absorbentcore is suitably sandwiched between a bodyside liner, and a liquidimpervious outer cover. Thus, in use, one of the surge management layersmay be located between the body of the wearer and the absorbent layer,while the other surge management layer will be located such that theabsorbent layer is between it and the body of the wearer. Either thefirst or second surge management layer can be located on the bodyside ofthe absorbent layer (between the absorbent layer and the body of thewearer during use).

In one embodiment of the present invention the first surge managementlayer is located, during use, between the absorbent layer and the bodyof the wearer. In this embodiment, the first surge management layercomprises from about 10 to about 100 weight percent of a syntheticpolymeric fiber formed from a high wet modulus polymeric material. Theweb is formed such that it possesses a relatively high degree ofstructural integrity. For example, the web can be formed by meltblowingor may be a bonded carded web. Such materials may generally possess arelatively high degree of wet resiliency. When the first surgemanagement layer is resilient, the fibrous web is able to maintain anopen porous structure while under a load, and to resist collapse whenwetted, such that it is able to receive subsequent insults.

Specifically, in one preferred embodiment, it is desired that the surgemanagement layer located between the body of a wearer and the absorbentlayer exhibits a wet resiliency factor of at least about 1.5, preferablyof at least about 1.7. The wet resiliency factor is determined bycompressing a wet sample of the surge management layer at a pressure of2.0 pounds per square inch for 60 minutes and then measuring the densityat the 2.0 pounds per square inch (13.19 kilopascal) loading. The sampleis then measured for density at a loading of 0.2 pound per square inch.The wet resiliency factor is determined by dividing the sample densityat 2.0 psi by the sample density at 0.2 psi.

When the second surge management layer is formed from more than 50weight percent of inherently hydrophilic fibers such as wood pulp fluff,the second surge management layer may be less resilient than the firstsurge management material comprising synthetic polymeric fibers. Whenthe second surge management layer is formed entirely from wood pulpfluff, the second surge management layer possesses a relatively lowdegree of wet resiliency.

Accordingly, in one embodiment of the present invention, the first surgemanagement layer is located between the body of a wearer and theabsorbent layer and comprises at least about 50 weight percent of asynthetic polymeric fiber. The second surge management layer is locatedon the opposite side of the absorbent layer and comprises at least about55 weight percent of a cellulosic fiber such as wood pulp fluff. Boththe first and second surge management layers function by holding surgesof liquid applied to the absorbent structure for a period of timesufficient for the absorbent layer to desorb the surge management layersand absorb and retain the liquid. In this manner, the surge managementlayers are able to receive subsequent insults of liquid (surges) andagain hold the liquid for a period of time sufficient for the liquid tobe absorbed by the absorbent layer.

A further advantage of locating the first surge management layer betweenthe body of a wearer and the absorbent layer is that the first surgemanagement material, may have a relatively dry feel even after it hasbeen wetted. This is because the first surge management layer includessynthetic polymeric fibers, is resilient and may be more easily desorbedby the absorbent layer than the second surge management layer. Thus, arelatively dry surface may be presented for contacting a wearer's skin.In contrast, the second surge management layer including cellulosic orother inherently hydrophilic fibers can have a relatively wet feel. Thiswet surface is located remote from the body of a wearer and is spacedtherefrom by the first surge management layer and the absorbent layer.

In order to assist the second surge management layer in performing itssurge management function when it is located with the absorbent layerand first surge management layer between it and the body of a wearer, itmay be desired to provide a liquid applied to the first surge managementlayer easy access to the second surge management layer. Accordingly, itmay be desired to provide the absorbent layer and/or first surgemanagement layer with areas of reduced basis weight or holes so that aliquid applied to the first surge management layer can pass through theareas of lower basis weight or the holes quickly and reach the secondsurge management layer. Alternatively, it may be desired to make thefirst surge management layer and/or absorbent layer smaller than thesecond surge management layer so that if a liquid applied to the firstsurge management layer and/or absorbent layer runs off of that layer, itthen comes into contact with the second surge management layer which iseither wider and/or longer than the first surge management layer or theabsorbent layer. It may also be possible to form the first surgemanagement layer and the absorbent layer with a low mass such that aliquid applied to the first surge management layer can pass through thefirst surge management layer and absorbent layer without completedissipation of kinetic energy. For example, the absorbent layer can beformed to have large free volume pathways in which free volume ismaintained even after initial wetting.

In one preferred embodiment, the absorbent layer is formed from anair-laid mixture of wood pulp fluff and high-absorbency material. Thehigh-absorbency material is contained in the air-laid wood pulp fluff.The mixture of wood pulp fluff and high-absorbency material is suitablyair-laid onto a porous forming surface through which a vacuum is drawn.The porous forming surface may be a forming wire or forming drum. Inorder to form holes or areas of reduced basis weight in the absorbentlayer, areas of the porous forming surface are blocked off so that avacuum is not drawn therethrough. These blocked off areas correspond tothe areas of reduced basis weight or holes in the absorbent layer. Theblocked off areas can be arranged in essentially any pattern desired. Inone embodiment, the blocked off areas are blocked off by 3-dimensionalprojections. For example, the areas may be blocked off by pyramidal orconically shaped projections. Alternatively, holes may be cut in theabsorbent layer by methods known to those skilled in the art.

The present invention can be understood by reference to the drawingswherein FIG. 1 illustrates a cross-sectional view of the absorbentstructure according to the present invention. Absorbent structure 10comprises a first surge management layer 12, an absorbent layer 14 and asecond surge management layer 16. The absorbent layer 14 is locatedbetween the first surge management layer 12 and the second surgemanagement layer 16.

As discussed above, the absorbent structures according to the presentinvention are suitable for use in absorbent products such as diapers.FIG. 2 illustrates an infant diaper embodying an absorbent structureaccording to the present invention. Diaper 20 typically includes aliquid-permeable bodyside liner 22; a substantially liquid-impermeableouter cover 24; an absorbent structure 26, positioned between the linerand outer cover; leg elastic members 28; and waist elastic members 30.The liner 22, outer cover 24, absorbent structure 26, and the elasticmembers 28 and 30 may be assembled in a variety of well-known diaperconfigurations. It should be recognized, however, that in articles otherthan diapers, individual components, such as the liner, outer cover, orelastic members, may be optional. The desirability of includingparticular components in other absorbent articles would depend on theintended end use of the absorbent article.

The absorbent structure 26 comprises a first surge management layer 32,a second surge management layer 34, and an absorbent layer 36 locatedbetween the surge management layers 32 and 34. As can be seen fromreference to FIG. 2 in the illustrated embodiment, the second surgemanagement layer 34 is larger than the absorbent layer 36 and the firstsurge management layer 32. Thus, if a liquid cannot be held or absorbedby the first surge management layer 32 or rapidly absorbed by theabsorbent layer 36, and the liquid runs off, it will come into contactwith the second surge management layer 34 and be maintained in theabsorbent structure. The diaper illustrated in FIG. 2 further comprisescontainment flaps 38 known to those skilled in the art and adhesive tapemembers 40 for attaching the diaper about the waist of an infant.

Those skilled in the art will recognize materials suited for use informing the components of the diaper illustrated in FIG. 2. Further, itis known that the components of the absorbent structure 26 may beindividually or collectively wrapped in a low basis weight material suchas a cellulosic wrap sheet (basis weight about 11 grams per squaremeter) or similar material.

If it is desired to impart the ability for the absorbent structureaccording to the present invention to perform a distribution function,it may be possible to provide either the first or second surgemanagement layer with the ability to distribute a liquid. Methods ofimparting the ability to distribute a liquid to fibrous webs are known.For example, when the second surge management layer is formed from woodpulp fluff, it may be possible to densify the wood pulp fluff eitheracross its entire width or to provide densified channels which arecapable of distributing a liquid.

When the absorbent layer comprises a relatively large concentration ofsuperabsorbent particles, it is sometimes difficult for a liquid appliedto one surface of the absorbent layer to pass through the absorbentlayer to the other surface. In order to facilitate the passage of liquidthrough the absorbent layer, Applicants have found that it is beneficialto provide the absorbent layer with a Z-gradient (direction normal tothe X-Y plane of the absorbent layer) particle size distribution. Thatis, if the high-absorbency material is in the form of particles orspheres having different maximum cross-sectional dimensions, it isdesired to place the larger particles on the bodyside of the absorbentlayer with the smaller particles located on the opposite side of theabsorbent layer. Such a configuration is illustrated in FIG. 3 which isa cross-sectional view of an absorbent layer according to the presentinvention illustrating such a Z-gradient particle size distribution.

TEST METHODS Absorbency Under Load

The Absorbency Under Load (AUL) is a test which measures the ability ofan absorbent material to absorb a liquid (0.9 weight percent solution ofsodium chloride in distilled water) while under an applied load orrestraining force.

Referring to FIG. 4, the apparatus and method for determining AUL willbe described. Shown is a perspective view of the apparatus in positionduring a test. Shown is a laboratory jack 101 having an adjustable knob102 for raising and lowering the platform 103. A laboratory stand 104supports a spring 105 connected to a modified thickness meter probe 106,which passes through the housing 107 of the meter, which is rigidlysupported by the laboratory stand. A plastic sample cup 108, whichcontains the high-absorbency (superabsorbent) material sample to betested, has a liquid-permeable bottom and rests within a petri dish 109,which contains the saline solution to be absorbed. A weight 110 rests ontop of a spacer disc (not visible) resting on top of the superabsorbentmaterial sample (not visible).

The sample cup consists of a plastic cylinder having a 1 inch insidediameter and an outside diameter of 1.25 inch. The bottom of the samplecup is formed by adhering a 100 mesh metal screen having 150 micronopenings to the end of the cylinder by heating the screen above themelting point of the plastic and pressing the plastic cylinder againstthe hot screen to melt the plastic and bond the screen to the plasticcylinder. Alternatively, the screen can be adhesively attached to theend of the cylinder.

The modified thickness meter used to measure the expansion of the samplewhile absorbing the saline solution is a Mitutoyo Digimatic Indicator,IDC Series 543, Model 543-180, having a range of 0-0.5 inch and anaccuracy of 0.00005 inch (Mitutoyo Corporation, 31-19, Shiba 5-chome,Minato-ku, Tokyo 108, Japan). As supplied from Mitutoyo Corporation, thethickness meter contains a spring attached to the probe within the meterhousing. This spring is removed to provide a free falling probe, whichhas a downward force of about 27 grams. In addition, the cap over thetop of the probe located on the top of the meter housing is also removedto enable attachment of the probe to the suspension spring 5 (availablefrom McMaster-Carr Supply Co., Chicago, Ill. Item No. 9640K41), whichserves to counter or reduce the downward force of the probe to about 1gram, ±0.5 gram. A wire hook can be glued to the top of the probe forattachment to the suspension spring. The bottom tip of the probe is alsoprovided with an extension needle (Mitutoyo Corporation, Part No.131279) to enable the probe to be inserted into the sample cup.

To carry out the test, a 0.160 gram sample of the high-absorbencymaterial, which has been sieved to a particle size between 300 and 600microns, is placed into the sample cup. The sample is then covered witha plastic spacer disc, weighing 4.4 grams, which is slightly smallerthan the inside diameter of the sample cup and serves to protect thesample from being disturbed during the test. The 100 grams weight isthen placed on top of the spacer disc, thereby applying a load of 0.3pound per square inch. The sample cup is placed in the petri dish on theplatform of the laboratory jack which is raised up until it contacts thetip of the probe. The meter is zeroed. A sufficient amount of salinesolution is added to the petri dish (50-100 milliliters) to begin thetest. The distance the weight is raised by the expanding sample as itabsorbs the saline solution is measured by the probe. This distance,multiplied by the cross-sectional area inside the sample cup, is ameasure of the expansion volume of the sample due to absorption.Factoring in the density of the saline solution and the weight of thesample, the amount of saline solution absorbed is readily calculated.The weight of saline solution absorbed after 60 minutes is the AULvalue, expressed as grams saline solution absorbed per gram ofhigh-absorbency material. If desired, the readings of the modifiedthickness meter can be continuously input to a computer (MitutoyoDigimatic Miniprocessor DP-2 DX) to make the calculations and provideAUL readings. As a cross-check, the AUL can also be determined bydetermining the weight difference between the sample cup before andafter the test, the weight difference being the amount of solutionabsorbed by the sample.

Fluid Run-Off Evaluation

The fluid run-off evaluation of composites according to the presentinvention and comparative composites is determined as follows.Specifically, the fluid run-off is determined by providing a samplewhich is 15 inches long and 4.5 inches wide. Referring to FIG. 5, thesample 302 is placed in a trough 300 having an included angle (alpha) of60 degrees. Trough 300 defines a slot 304 extending across the entirewidth of the trough 300 at its lowest point. The trough 300 is at least4 inches wider than the sample 302 to be tested. A collection device(not pictured) is placed under trough 300 to collect fluid which passesout of trough 300 through slot 304. FIG. 6 is a cross-sectional viewtaken along line 6--6 of FIG. 5. As can be seen from reference to FIG.6, test fluid is delivered to the sample 302 to be tested from a nozzle306 having a 3 millimeter diameter (a) which is attached to aperistaltic pump equipped with a pulse suppressor. The nozzle is placeda distance (b) of 6.4 millimeters from the surface of the sample to betested at a distance (c) of about 5.5 inches from the end of the sampleto be tested such that the nozzle is generally perpendicular to theimmediate adjacent surface of the sample 302 to be tested. Thispositioning should be maintained throughout the test. The sample to betested is subjected to ten 60 milliliter insults of synthetic urine. Theurine is applied through the nozzle 306 at a rate of approximately 15millimeters per second and a velocity of about 210 centimeters persecond. Each of the ten 60 milliliter insults is applied 15 minutesafter the immediately preceding insult. The amount of fluid which passesthrough slot 304 and is collected in the collection device, is weighed(in grams), and is reported for each insult. As a general rule, thelower the amount of run-off per insult, the better the composite wouldbe expected to perform in an absorbent product. The synthetic urinecomposition referenced herein comprises 0.31 grams monobasic calciumphosphate monohydrate (CaH₄ (PO₄)₂ H₂ O), 0.68 grams monobasic potassiumphosphate (KH₂ PO₄), 0.48 grams magnesium sulphate heptahydrate (MgSO₄7H₂ O), 1.33 grams potassium sulphate (K₂ SO₄), 1.24 grams tribasicsodium phosphate dodecahydrate Na₃ PO₄ 12H₂ O), 4.4 grams sodiumchloride (NaCl), 3.16 grams potassium chloride (KCl), 8.56 grams of urea(CO)NH₂)₂, 0.1 grams pluronic 10R8 surfactant (a non-ionic surfactantcommercially available from BASF Wyandotte Corporation) and 1 grammethyl paraben and 1 gram germall 115 preservative (commerciallyavailable from Santell Chemical Company, Chicago, Ill.) per liter usingdistilled water as a solvent. The components are added to 900milliliters of distilled water in the order given and each dissolvedbefore the next component is added. The solution is finally diluted to 1liter. The solution is found to have a surface tension of 55 dynes persquare centimeter.

EXAMPLES

The following materials are employed as first surge management layers.

Sample A--A bonded carded web formed from 60 weight percent of a 5.5denier per filament polyester fiber commercially available from theTennessee Eastman Company, Kingsport, Tenn., and 40 weight percent of a2.25 denier per filament polyester fiber commercially available fromHoechst-Celanese, Spartansburg, S.C., under the trade designation T291.The bonded carded web is commercially available from Bonnar Fabrics,Greenville, S.C. The carded web formed from the fibers described aboveis bonded with 18 weight percent, based on total web weight, of apolyester binder powder commercially available from EMS-Chemie,Switzerland, under the trade designation EMS D1287 polyester binderpowder. The bonded carded web has a basis weight of 50 grams per squaremeter and a density of about 0.044 grams per cubic centimeter.

Sample B--A bonded carded web formed from 60 weight percent of a 6.0denier per filament polyester teraphthalate fiber commercially availablefrom Hoechst-Celanese under the trade designation T295 and 40 weightpercent of a 1.8 denier per filament sheath core (polyethylenesheath/polyethylene teraphthalate core) bicomponent fiber commerciallyavailable from BASF Corporation, Fibers Division, Williamsburg, Va.,which carded web is bonded through a through-air bonding process. Theweb has a basis weight of about 50 grams per square meter and a densityof about 0.044 grams per cubic centimeter.

Sample C--A fibrous web of side-by-side spunbond bicomponent fibersformed from polyethylene and polypropylene (50/50). The side-by-sidebicomponent fibers have a thickness of 3.0 denier per filament. Thespunbonded web is through-air bonded. The web has a basis weight of 54grams per square meter and a density of 0.032 gram per cubic centimeter.The web is employed with the wire side up (closest to nozzle 306 duringtesting).

Sample D--A web is formed as described in connection with Sample C,except that the web is employed with the face side up.

Sample E--An air-formed web is formed comprising 50 weight percent of a6.5 denier per filament polyethylene teraphthalate fiber commerciallyavailable from Tennessee Eastman under the trade designation Kodel® 431and 50 weight percent of a 3.3 denier per filamentpolyethylene/polypropylene bicomponent fiber (polyethylenesheath/polypropylene core) fiber having a 6 millimeter lengthcommercially available from Danaklon A/S, Denmark. The air-formed web isthrough-air bonded at a temperature sufficient to melt the polyethylenesheath of the bicomponent fiber. The web formed has a basis weight of 58grams per square meter and a density of 0.026 gram per cubic centimeter.

Sample F--An airlaid web comprising 50 weight percent of wood pulp flufffibers commercially available from Weyerhaeuser Company, Tacoma, Wash.,under the trade designation NF-105, and 50 weight percent of apolypropylene meltblown fiber having a diameter of about 10 micrometers.The airformed web has a basis weight of about 75 grams per square meterand a density of about 0.048 grams per cubic centimeter.

Sample G--An airlaid web comprising wood pulp fluff and polypropylenemeltblown fibers is formed as described above, except the web is formedto have a basis weight of 125 grams per square meter and a density of0.05 grams per cubic centimeter.

The second surge management layer comprises an airlaid batt of wood pulpfluff commercially available from the Kimberly-Clark Corporation underthe trade designation CR-54 (20 percent hardwood, 80 percent softwood).The airlaid batt has a basis weight of 115 grams per square meter and adensity of 0.12 gram per cubic centimeter. The absorbent layer is formedcomprising 70 weight percent of a high-absorbency superabsorbentmaterial commercially available from Hoechst-Celanese under the tradedesignation IM-5000P; 17 weight percent of a wood pulp fluffcommercially available from Kimberly-Clark Corporation under the tradedesignation CR-54; and about 13 weight percent water. The absorbentlayer is airlaid on a cellulose wrap sheet having a basis weight ofabout 11 grams per square meter. A 4-inch wide strip of the wood pulpfluff, superabsorbent material, and water is formed on a 7-inch widecellulose wrap sheet. A 31/2-inch wide cellulose wrap sheet is laid ontop of the mixture of fluff and superabsorbent with the extra width ofthe lower wrap sheet being folded over the edges of the mixture of fluffand superabsorbent to form a completely enclosed absorbent layer. Thecomponents of wood pulp fluff, superabsorbent material and water areformed on the lower wrap sheet in the following sequence: wood pulpfluff, superabsorbent material, and water. As formed, the superabsorbentparticles having a larger particle diameter segregate on the side of theabsorbent core nearest the 31/2-inch wide cellulose wrap sheet. Thisside of the absorbent layer faces up. The absorbent layer has a basisweight of about 452 grams per square meter and a density of about 0.25gram per cubic centimeter. After formation, the absorbent layer isallowed to come to equilibrium by being exposed to ambient conditionsfor a period of about 30 days.

In forming the composites of the present invention, a first surgemanagement material selected from the samples described above is pliedwith an absorbent layer and the second surge management layer describedabove. The absorbent layer is located between the first surge managementlayer and the second surge management layer with the first surgemanagement layer being located closest to nozzle 306 during testing. The3-ply composites are then placed on a polyethylene film having athickness of 1 mil and samples which are 15 inches long and 4 incheswide cut from the composites. The samples thus prepared are subjected tothe fluid runoff evaluation test as described above. As the absorbentlayer and second surge management layer are the same in each of thecomposites, the composites are identified by the first surge managementmaterial employed. It is understood that each of the samples comprisenot only the first surge management layer but also an absorbent layer, asecond surge management layer, and the lower polyethylene film backing.The results of the fluid runoff evaluation are set forth in Table 1.

TABLE 1

                                      TABLE 1                                     __________________________________________________________________________    Runoff (grams)                                                                Insult No.                                                                    Sample                                                                              1   2  3   4  5   6  7   8  9   10                                      __________________________________________________________________________    A     0.55                                                                              0.16                                                                             3.50                                                                              7.99                                                                             15.29                                                                             18.35                                                                            24.94                                                                             31.31                                                                            37.28                                                                             39.77                                   B     0.06                                                                              0.18                                                                             1.90                                                                              4.68                                                                             10.28                                                                             18.75                                                                            27.31                                                                             33.83                                                                            39.05                                                                             43.02                                   C     0   0  2.03                                                                              5.98                                                                             11.37                                                                             19.03                                                                            28.03                                                                             35.94                                                                            40.17                                                                             43.84                                   D     0.49                                                                              0.78                                                                             4.16                                                                              8.14                                                                             10.94                                                                             19.27                                                                            27.00                                                                             31.35                                                                            37.11                                                                             40.48                                   E     2.65                                                                              0  1.56                                                                              4.82                                                                             7.46                                                                              13.82                                                                            23.03                                                                             30.99                                                                            36.24                                                                             40.47                                   F     0.03                                                                              1.55                                                                             3.93                                                                              8.26                                                                             14.76                                                                             21.62                                                                            28.70                                                                             34.68                                                                            40.42                                                                             43.59                                   G     0   0.72                                                                             2.07                                                                              5.17                                                                             11.47                                                                             21.28                                                                            29.93                                                                             34.68                                                                            39.89                                                                             42.37                                   Absorbent.sup.1                                                                     4.12                                                                              4.58                                                                             6.59                                                                              9.67                                                                             14.06                                                                             18.94                                                                            25.10                                                                             30.17                                                                            32.94                                                                             38.67                                   __________________________________________________________________________     .sup.1 Absorbent layer and second surge management layer tested alone,        with no first surge management layer.                                    

For comparison purposes, the composites comprising a first surgemanagement material from the materials described above, and an absorbentlayer are formed on the polyethylene film backing. These composites donot comprise the second surge management layer and do not represent thepresent invention. These composites (also identified by the compositionof the first surge management layer) are subjected to the fluid runoffevaluation test. The results are set forth in Table 2.

TABLE 2

                                      TABLE 1                                     __________________________________________________________________________    Runoff (grams)                                                                Insult No.                                                                    Sample                                                                              1   2  3   4  5   6  7   8  9   10                                      __________________________________________________________________________    A     3.71                                                                              0.76                                                                             3.50                                                                              9.03                                                                             15.43                                                                             22.67                                                                            29.77                                                                             34.06                                                                            38.16                                                                             42.86                                   B     3.82                                                                              0.25                                                                             2.61                                                                              7.32                                                                             14.19                                                                             21.15                                                                            28.84                                                                             35.52                                                                            39.83                                                                             43.13                                   C     3.59                                                                              0.85                                                                             3.36                                                                              7.23                                                                             12.93                                                                             23.09                                                                            29.58                                                                             36.05                                                                            40.01                                                                             43.06                                   D     3.79                                                                              1.62                                                                             4.94                                                                              10.31                                                                            18.56                                                                             27.95                                                                            34.05                                                                             36.74                                                                            40.55                                                                             40.93                                   E     8.04                                                                              1.79                                                                             2.66                                                                              7.60                                                                             13.77                                                                             20.85                                                                            28.83                                                                             34.31                                                                            39.44                                                                             43.16                                   F     2.15                                                                              1.85                                                                             6.54                                                                              14.69                                                                            22.32                                                                             30.34                                                                            35.65                                                                             39.15                                                                            43.59                                                                             46.04                                   G     0.02                                                                              0.11                                                                             1.59                                                                              8.28                                                                             17.14                                                                             26.08                                                                            32.50                                                                             37.47                                                                            41.97                                                                             45.21                                   Absorbent.sup.1                                                                     7.71                                                                              14.33                                                                            11.16                                                                             17.46                                                                            21.5                                                                              23.68                                                                            27.50                                                                             30.48                                                                            34.39                                                                             37.83                                   __________________________________________________________________________     .sup.1 Absorbent layer tested alone, with no first or second surge            management layers.                                                       

As can be seen from reference to Tables 1 and 2, the presence of thesecond surge management layer greatly improves the performance of thetest composites in the fluid runoff evaluation test. Naturally, thelower the fluid runoff, the better the expected performance of thecomposite in an absorbent article such as a diaper. Moreover, it is seenthat first surge management layers comprising a relatively highconcentration of synthetic polymeric material fibers perform better thana first surge management layer comprising up to 50 weight percent ofwood pulp fluff (without going to significantly higher basis weight).

FIGS. 7 and 8 graphically illustrate the results set forth in Tables 1and 2, respectively. As can be seen from reference to FIGS. 7 and 8, thevarious bar graphs represent the runoff for the first insult, and theaverage runoff per insult for the first three insults and the first sixinsults.

While the invention has been described in detail with respect tospecific embodiments thereof, it will be appreciated that those skilledin the art, upon attaining an understanding of the foregoing, mayreadily conceive of alterations to, variations of, and equivalents tothose embodiments. Accordingly, the scope of the present inventionshould be assessed as that of the appended claims and any equivalentsthereto.

What is claimed is:
 1. An absorbent structure, said absorbent structurecomprising:a first surge management layer comprising a fibrous web, saidweb comprising synthetic polymeric fibers, said first surge managementlayer having a basis weight of from about 20 to about 200 grams persquare meter, and a density of from about 0.01 to about 0.12 gram percubic centimeter; a second surge management layer comprising a fibrousweb, said web comprising hydrophilic fibers, said second surgemanagement layer having a basis weight of from about 20 to about 200grams per square meter and a density of from about 0.04 to about 0.2gram per cubic centimeter; and an absorbent layer located between and inliquid communication with said first and second surge management layers,said absorbent layer comprising means for containing a high-absorbencymaterial and from about 50 to about 100 weight percent, based on totalweight of said absorbent layer, of a high-absorbency material containedby said means for containing a high-absorbency material, said absorbentlayer having a basis weight of from about 200 to about 1000 grams persquare meter and a density of from about 0.06 to about 0.4 gram percubic centimeter wherein the density of said absorbent layer is greaterthan the density of said first and second surge management layers andthe density of the first surge management layer is different than thedensity of said second surge management layer.
 2. The absorbentstructure according to claim 1 wherein said first surge management layeris, in use, located between the body of a wearer and the absorbentlayer.
 3. The absorbent structure according to claim 1 wherein saidfirst surge management layer comprises from about 10 to 100 weightpercent synthetic polymeric fibers.
 4. The absorbent structure accordingto claim 3 wherein said first surge management layer is formed by amethod selected from the group consisting of meltblowing, spunbonding,carding, and airlaying.
 5. The absorbent structure according to claim 4wherein said synthetic polymeric fibers are formed from a materialselected from the group consisting of polyolefins, polyesters,polyamides, and acrylics.
 6. The absorbent structure according to claim1 wherein said first surge management layer has a basis weight of fromabout 30 to about 150 grams per square meter.
 7. The absorbent structureaccording to claim 1 wherein said second surge management layercomprises from 10 to 100 weight percent of hydrophilic fibers.
 8. Theabsorbent structure according to claim 7 wherein said second surgemanagement layer comprises 100 weight percent of cellulosic fibers. 9.The absorbent structure according to claim 1 wherein said second surgemanagement layer has a basis weight of about 50 to about 150 grams persquare meter.
 10. The absorbent structure according to claim 1 whereinsaid absorbent layer comprises from about 60 to about 95 weight percentof a high-absorbency material contained by said means for containing ahigh-absorbency material.
 11. The absorbent structure according to claim10 wherein said absorbent layer comprises from about 70 to about 90weight percent of a high-absorbency material contained by said means forcontaining a high-absorbency material.
 12. The absorbent structureaccording to claim 1 wherein said absorbent layer has a basis weight offrom about 250 to about 750 grams per square meter.
 13. The absorbentstructure according to claim 1 wherein the density of said absorbentlayer is at least about 20 percent greater than the density of both ofsaid first and second surge management layers.
 14. The absorbentstructure according to claim 13 wherein the density of said absorbentlayer is at least about 30 percent greater than the density of both ofsaid first and second surge management layers.
 15. The absorbentstructure according to claim 2 wherein the density of the first surgemanagement layer is less than the density of the second surge managementlayer.
 16. The absorbent structure according to claim 1 wherein thedensity of the first and second surge management layers differ by atleast about 20 percent of the density of the lowest density layer. 17.The absorbent structure according to claim 1 wherein said absorbentlayer defines holes.
 18. The absorbent structure according to claim 1wherein said absorbent layer comprises areas of reduced basis weight.19. The absorbent structure according to claim 1 wherein said highabsorbency material is in the form of particles or spheres havingdifferent maximum cross-sectional dimensions with the larger particleslocated on the side of the absorbent layer closest to a wearer in use.20. An absorbent structure, said structure comprising a first surgemanagement layer, said first surge management layer comprising a fibrousweb, said fibrous web comprising from about 50 to 100 weight percent ofsynthetic polymeric fibers formed from an inherently hydrophobicpolymeric material, said first surge management layer having a basisweight of from about 30 to about 150 grams per square meter and adensity of from about 0.015 to about 0.1 grams per cubic centimeter;asecond surge management layer, said second surge management layercomprising a fibrous web, said fibrous web comprising from about 55 toabout 100 weight percent hydrophilic fibers, said second surgemanagement layer having a basis weight of from about 50 to about 150grams per square meter, and a density of from about 0.06 to about 0.16grams per cubic centimeter; and an absorbent layer located between andin liquid communication with said first and second surge managementlayers, said absorbent layer comprising means for containing ahigh-absorbency material and from about 50 to about 100 weight percent,based on total weight of the absorbent layer, of a high-absorbencymaterial contained by said means for containing a high-absorbencymaterial, said absorbent layer having a basis weight of from about 250to about 750 grams per square meter and a density of from about 0.12 toabout 0.35 gram per cubic centimeter wherein the density of saidabsorbent layer is greater than the density of both of said first andsecond surge management layers, and the densities of the first andsecond surge management layers are different.
 21. An absorbent product,said absorbent product comprising:a liquid-impermeable bodyside liner; asubstantially liquid-impermeable outer cover; and an absorbent structurelocated between said liner and outer cover said absorbent structurecomprising: a first surge management layer comprising a fibrous web,said web comprising synthetic polymeric fibers, said first surgemanagement layer having a basis weight of from about 20 to about 200grams per square meter, and a density of from about 0.01 to about 0.12grams per cubic centimeter; a second surge management layer comprising afibrous web, said web comprising hydrophilic fibers, said second surgemanagement layer having a basis weight of from about 20 to about 200grams per square meter and a density of from about 0.04 to about 0.2gram per cubic centimeter; and an absorbent layer located between and inliquid communication with said first and second surge management layers,said absorbent layer comprising means for containing a high-absorbencymaterial and from about 50 to about 100 weight percent, based on totalweight of said absorbent layer, of a high-absorbency material containedby said means for containing a high-absorbency material, said absorbentlayer having a basis weight of from about 200 to about 1000 grams persquare meter and a density of from about 0.06 to about 0.4 gram percubic centimeter wherein the density of said absorbent layer is greaterthan the density of said first and second surge management layers andthe density of the first surge management layer is different than thedensity of said second surge management layer.
 22. The absorbent productaccording to claim 21 wherein said first surge management layer islocated between said bodyside liner and said absorbent structure.
 23. Anabsorbent structure, said absorbent structure comprising:a first surgemanagement layer comprising a fibrous web, said web comprising syntheticpolymeric fibers, said first surge management layer having a basisweight of from about 20 to about 200 grams per square meter, and adensity of from about 0.01 to about 0.12 gram per cubic centimeter; asecond surge management layer comprising a fibrous web, said webcomprising hydrophilic fibers, said second surge management layer havinga basis weight of from about 20 to about 200 grams per square meter anda density of from about 0.04 to about 0.2 gram per cubic centimeter; andan absorbent layer located between and in liquid communication with saidfirst and second surge management layers, said absorbent layercomprising a fibrous web containing from about 50 to about 100 weightpercent, based on total weight of said absorbent layer, of ahigh-absorbency material, said absorbent layer having a basis weight offrom about 200 to about 1000 grams per square meter and a density offrom about 0.06 to about 0.4 gram per cubic centimeter wherein thedensity of said absorbent layer is greater than the density of saidfirst and second surge management layers and the density of the firstsurge management layer is different than the density of said secondsurge management layer.